The present invention relates to image processing in a computing system and more particularly, to a method for enhancing the quality of digital images.
Digital images are commonly used in today""s computing world. However, the quality of these images vary widely. For example, some digital images are highly compressed JPEG files with artifacts, but others are of a very high quality. The inherent variation in the quality of digital images poses a challenge for image rendering devices, such as printers and computer monitors to accurately reproduce digital images.
Prior image processing techniques have been proposed for improving the quality of digital images. Conventional algorithms have been used for suppressing compression artifacts and also for restoring images that are distorted by various types of noise. However, applying an algorithm for suppressing compression artifacts to an image that does not have any artifacts will result in a degraded image. For example, if an algorithm for reducing JPEG artifacts is applied to a sharp image that does not have JPEG artifacts, it will result in a blurry image compared to the original image.
Other conventional image processing techniques have been proposed for enhancing images without excessive artifacts. Examples of such techniques are, unsharp masking algorithms for image sharpening and histogram transformations for enhancing image contrast. However, application of the foregoing processes to an image that does include artifacts will also result in image distortion.
Therefore, what is desired is a method for improving the quality of digital images with or without artifacts resulting in an enhanced image.
The present invention addresses the foregoing by providing a method for improving arbitrary digital images with an input pixel window having an input pixel, including process steps to calculate variation in luminance of the pixel window, compare the variation in the luminance of the pixel window to a predetermined first threshold value and process the input pixel based upon the comparison. Thereafter, output pixel with pixel value equal to the input pixel values, if the luminance is less than the first threshold value; apply a moderate smoothing filter if the variation in luminance is greater than the first threshold value and less than a second predetermined threshold value; and apply a non-linear, enhancement filter if the luminance variation is greater than the second threshold value.
By virtue of the foregoing aspects of the present invention, a filter is applied to a digital image based upon image content and that improves the quality of reproduced digital images.